A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 1888320 can be evenly divided by 1 2 3 4 5 6 7 8 10 12 14 15 16 20 21 24 28 30 32 35 40 42 48 56 60 64 70 80 84 96 105 112 120 140 160 168 192 210 224 240 280 281 320 336 420 448 480 560 562 672 840 843 960 1,120 1,124 1,344 1,405 1,680 1,686 1,967 2,240 2,248 2,810 3,360 3,372 3,934 4,215 4,496 5,620 5,901 6,720 6,744 7,868 8,430 8,992 9,835 11,240 11,802 13,488 15,736 16,860 17,984 19,670 22,480 23,604 26,976 29,505 31,472 33,720 39,340 44,960 47,208 53,952 59,010 62,944 67,440 78,680 89,920 94,416 118,020 125,888 134,880 157,360 188,832 236,040 269,760 314,720 377,664 472,080 629,440 944,160 and 1,888,320, with no remainder.
Since 1,888,320 cannot be divided by just 1 and 1,888,320, it is not a prime number.